The ultimate object of a study on cancers is in the research and discovery of carcinostatic and cancericidal substances, as well as in the determination of early detection of cancers or early diagnosis thereof. Various medicines, therapeutic protocols and reagents for cancers have heretofore been developed, all of which are, however, disadvantageous since they affect not only cancer cells but also normal tissues and normal cells. Accordingly, conventional medicines and reagents are, even though they are very effective, extremely limited in their application, due to the severe side effects thereof.
An immunological reaction (antigen-antibody reaction) is a highly specific reaction. However, it was difficult, using conventional polyclonal antibodies, to recognize such antigens as being differentiated on the basis of an extremely minor antigenic determinant, such as subsets of lymphocytes, even though the absorption operation is repeated many times. A monoclonal antibody developed by Milstein, et al. (Koeler, G. and Milstein, C.: Nature, 256, 495 (1975)) has overcome the obstacle; and is expected to provide such medicines capable of specifically killing cancer cells only, without imparting any damage to other normal cells by preparing a monoclonal antibody capable of specifically recognizing a cancer-specific antigen or a cancer-associated antigen on the cancer cells. In addition, it is considered that a diagnostic agent or a detecting agent using such a monoclonal antibody is free from any cross-reaction with normal serum components and that the detection of cancer-associated antigens and cancer-specific antigens will therefore be possible with high sensitivity.